Gear made of resin, and mold structure

Abstract

A gear made of a resin includes a substantially cylindrical rim having a plurality of teeth formed around an outer periphery thereof, a boss formed about a rotational center of the rim, and a web connecting the boss and the rim to each other. At least one groove is defined along outer surface of each tooth to divide the tooth in a widthwise direction of the tooth. As a result, a portion of the gear, in which the grooves are defined, is deformed in a reduced amount, leading to a reduced amount of deformation such as a warpage or sink in the entire gear, thereby providing an enhancement in tooth flank accuracy. Since the grooves are defined along the outer surfaces of the teeth, a lubricant such as grease can be supplied effectively to tooth flanks by previously applying the lubricant in the grooves.

1. A single gear made of resin, comprising a substantially cylindrical rim having a plurality of teeth formed around an outer periphery thereof with each of said plurality of teeth having front and rear facing surfaces and a top, a boss formed about a rotational center of said rim, and a web connecting said boss and said rim to each other, wherein
 at least one groove is defined along an entire outer peripheral surface of each tooth of said teeth, said at least one groove being provided in said outer peripheral surface of each of said front and rear facing surfaces and said top of each of said plurality of teeth and in a valley provided between each successive ones of said plurality of teeth, said at least one groove defining at least a central gear portion and at least two outer gear portions wherein said central gear portion comprises central gear teeth smaller than outer gear teeth of said two outer gear portions.  
 
   
   
     2. The single gear of  claim 1 , wherein the groove is formed at substantially the center in the widthwise direction of the teeth. 
   
   
     3. The single gear of  claim 1 , wherein a plurality of said groves are provided along the outer surface of the teeth.